Recently, the development of the backbone network communication line as mainly focusing on the optical fiber communication technology is proceeding steadily and, in such a situation, the electronic wirings in the information terminal are becoming a bottleneck. Against such background, instead of the conventional electric circuit substrate in which all signal transmissions are made by using the electric signal, the optoelectronic composite substrate (the optical waveguide device) of the type that transmits high-speed parts by the light has been proposed, in order to compensate the limit of transmission speed of the electric signal.
In the optoelectronic composite substrate, the light signal is transmitted by the optical waveguide including such a structure in which the core layer is surrounded by the cladding layers.
In an example of the method of manufacturing the optical waveguide, first, the lower cladding layer, the core layer, and the upper cladding layer are formed sequentially on the substrate. Then, the core layer is processed by the rotary blade so as to divide the core layer from the upper cladding layer, so that the groove portions each having an inclined surface at an angle of 45° to the light propagation direction are formed.
Then, in the air boundary of the inclined surface in the groove portion, the light which is propagated through the core layer is made to reflect in the vertical direction, and the light path is converted.
A related art is disclosed in Japanese Laid-open Patent Publication No. 2010-78882.
In the prior art, the groove portions each having the inclined surface are formed as the release spaces that are extended elongately to intersect orthogonally with a plurality of core layers such that these release spaces go across the optical waveguide forming areas, after the core layers are covered with the upper cladding layer. Accordingly, since a volume of the groove portions becomes relatively large, the enough mechanical strength of the optical waveguide cannot be obtained. Also, since the groove portions are connected elongately, such a risk is increased that a foreign matter adheres to the inclined surfaces, thereby long-term reliability of the optical waveguide is feared.
Further, in the case that the groove portions are covered by fixing the coating member onto the optical waveguide by the adhesive, some devising is needed such that the adhesive does not go around the groove portions.